Voicing for a computor organ

ABSTRACT

In a computor organ of the type wherein a musical waveshape is synthesized by computing in real time the amplitude contributions of the constituent Fourier components and summing these to obtain each waveshape sample point amplitude, the tonal quality or voice of the produced note is established by a set of harmonic coefficients that specify the relative amplitude of each Fourier component. Herein circuitry is disclosed for modifying the harmonic coefficient values to accomplish transient voice insertion including &#39;&#39;&#39;&#39;chiff&#39;&#39;&#39;&#39; and percussive transients, to modulate the harmonic content as a function of time during attack and decay, and to facilitate the external insertion of additional voices for the instrument.

United States Patent Deutsch 1 1 Oct. 21 1975 [54] VOICING FOR ACOMPUTOR ORGAN 3,809,792 5/1974 Deutsch 84/1124 v 3,821,714 6/1974Tomisuwa c1111.... 84/101 X [75] 'l Sherman 3,823,390 7/1974 Tomisawa etal 84/101 x C3115 3,831,015 8/1974 Hoff, Jr 114/1111 x Assignee: Nipponseizo Kabushiki Tomtsawa 8121i 1 1 1 Kaisha, Hamamatsu, Japan OTHERPUBLICA'HONS Filed; May 16, 1974 Ralph W. Burhans, Digital ToneSynthesis, Journal of the Audio En ineerin Society. Vol. 19, N0. 8, Se[21] Appl. No. 470,628 g g P tember 1971, pp. 660-663.

[52] U.S. Cl. 84/l.19; 84/1.11;84/l.13; Primary Examiner stephen J-Tomsky 5 1 C12 84/126 Assistant ExaminerStanley J. Witkowski 1] nt. GH1/02, 6101! 5/00 Alromey Agem or FirmfiHoward A. Sub. [58] F1eld ofSearch ..84/1.01, 1,03, 1.11, 1.13, 84/119, 1.22-1.26, DIG. 4, DIG. 5

[ ABSTRACT [56] References Cited In a computor organ of the type whereina musical UNITED STATES PATENTS waveshape is synthesized by computing inreal time 3,515,792 6/1970 Deutsch 114 103 the amplitude Contributionsof the Constituent Fourier 3,610,799 10/1971 Watson H 34/11 componentsand summing these to obtain each wave- 3,610,805 10/1971 Watson et al...84/113 Shape sample point amplitude, the tonal quality or 3,610,80610/1971 Deutsch 84/126 voice of the produced note is established by aset of 3,740,450 6/1973 Deutschm, 84/12 harmonic coefficients thatspecify the relative amplitj q tude of each Fourier component. Hereincircuitry is 1 1 1 d th 1 l- 3,757,022 9/1973 Markowitz 84/125 R, d p dr h h g 3,763,364 10/1973 Deutsch et :11 84/103 x C Percusswetrilnslemsg t C 3,394,748 2,1974 Deulsch n 84/124 monic content asafunct1on of time during attack and 3,809,786 5/1974 DCUISCh- 84/101decay, and to facilitate the external insertion of addi- 3,809,7885/1974 Deutschu. 84/101 tional voices for the instrument.

3,809,789 5/1974 Deutsch.,. 84/1101 3,809,790 5/1974 Deutsch 134 101 26Clalms- 13 Drawmg Figures 47 J MM," Fae 327,1 3 7 a2 cc. nl-rAcx/oscw5cm. 5ft) 'f unnmomc DMPLITUBI I I cwm ACTOR HIMORY Cw MULT'PUIRAccuMuLnYoR cuml V 4 I am 1 32 smuoon: my; fa l HaRMomc l man'm. TO icfizsxvuf f a mse cozczfnn TRansmn-r DICQDIR a, I new 12 l 3:; MEMORYaccess 30 nq' I CONTROL U36 HARMONK'; l INTIRVHL .sounu 5 l ADDKR \dm5YSTEM 1 62 7; 19 I7 1 R o 1 4 .4] 1 g u 7] 4 monucow 26 1 Yflnuslswrm iZ L INTEPVRL k DURQ'YION I ADDED 1 72 COUNTER 70a J 32:; t, MowLo 2w 1 J7 an 59 j L2, 54 L v a C1 UM N MACK] D x -50 EJ550212; 333 iifif-Sr?5WtTCHE$ OG c1 Mirna? Y Dl qullD L U.S. Patent Oct. 21, 1975 Sheet 1 of7 3,913,442

.rchffl.

" TIME T2 US. Patent Oct. 21, 1975 Sheet 2 of7 3,913,442

U.S. Patent Oct. 21, 1975 QQMONIC COEFFICIENT ADDER T scnLER D I C" 58 numzmomc COEFFICIENT MEMoQY /a Sheet 3 of 7 37 ADDER I 2 f RANDOM I74 /I7 7 ACCESS DATA HARMONIC HnRMomc COEFFICIENT COEFFICIENT MEM o R Y ENTERnm-A IN-EEIGIZLEO N MEMORY MEMoRv 0 7 f 172 MEMORY MEMORY QCCESS RagaCONT ROL com R L L MEMORY n a ACCESS J76 CONTQOL COUNTER lg MODLJLO wREAD ONLY CLOCK MEMORY US. Patent Oct. 21, 1975 Sheet 4 of7 3,913,442

US. Patent Oct. 21, 1975 Sheet 5 of7 3,913,442

O 0 y u 0 a o w 0 US. Patent Oct.21,1975 Sheet 7 of? 3,913,442

1 VOICING FOR A COMPUTOR ORGAN BACKGROUND OF THE INVENTION 1. Field ofthe Invention The present invention relates to improvements in voicingof an electronic musical instrument, and particularly to systems forintroducing chiff and other transient voice effects, for modulating theharmonic content of the generated tones as a function of time duringattack and decay, and for providing additional voices for a computororgan.

2. Related Applications The present invention is related to theapplicants copending U.S. patent application entitled COMPUTOR ORGAN,No. 225,883, filed Feb. 14, 1972, now U.S. Pat. No. 3,809,786.

3. Description of the Prior Art In a COMPUTOR ORGAN of the typedescribed in the above mentioned related application, musical tones aregenerated by computing the amplitudes at successive sample points of amusical waveshape and converting these to tones as the computations arecarried out in real time. Each sample point amplitude is obtained bysumming a set of individually evaluated constituent Fourier components.The tonal quality or voice of the produced sound is determined by therelative amplitudes of the constituent Fourier components, asestablished by a set of harmonic coefficients used in the calculations.The present invention concerns alterations in voicing of the producedtones.

A desirable feature in electronic entertainment organs is a so calledpercussive voice." This is a composite voice including a first tonehaving a piano-like at tack/decay envelope played in combination with anor gan-like substained tone. The effect is that of a percussive sound atthe onset of tonal production.

One object of the present invention is to implement the production ofsuch percussive tones in a computor organ. More generally, an objectiveis to implement a wide variety of percussive-like transient voices" inan electronic musical instrument.

One particular transient effect is called chiff." In a pipe organ, chiffoccurs during the attack, as the pipe produces a predominant sound atthe third or fifth harmonic. This predominant harmonic quicklydiminishes in relative intensity as the nominal pitch for that pipebegins to speak distinctly.

Electronic organs imitate chiff by playing a short grace note at theonset of tone production. The grace note is generated by actuating a 2%-f001 coupler for the duration of the nominal attack time for the8-foot tone which is to be chiffed. Customarily, chiff is used only ondiapason and flute tones.

The inventors U.S. Pat. No. 3,740,450 discloses apparatus for producingchiff tones in a digital organ of the type wherein a musical waveshapeis repetitively read out from storage at a rate related to the selectednote. A chiffing waveshape is stored in a separate memory that isaccessed during the attack portion of the primary tone. The separatewaveshape memory outputs are combined to produce the chiffed musicaltone.

Another object of the present invention is to implement chiff in acomputor organ by emphasizing certain constituent Fourier componentsincluded in the real time waveshape synthesis. Another desirable voicingeffect concerns modulation of the harmonic content during attack anddecay. In many natural musical instruments the harmonic content changesas a function of time. Thus during the attack, at the beginning of noteproduction, the high frequency harmonics may predominate. Gradually thelower order harmonics increase their contribution to the total soundenergy, until finally the characteristic voice is achieved. Simi larly,during decay, the lower order components die out faster than theharmonics of higher frequency. Another object of the present inventionis to implement such time dependent frequency modulation during attackand decay of tones produced by a computor organ.

The number of different voices available in a commercial electronicorgan typically is very limited. This is particularly true ininstruments of the type wherein tones are generated by sets ofoscillators together with filters for emphasizing or eliminating certainhigher harmonics. In a computor organ of the type described in the abovementioned U.S. Pat. No. 3,809,786 each voice is established by a set ofharmonic coefficients that specify the relative contribution of eachFourier component. Different voices can be achieved merely by utilizingdifferent sets of harmonic coefficients in the waveshape computation. Tothis end, another object of the present invention is to provide meansfor changing or introducing new sets of harmonic coefficients into thecomputor organ, so as to give the musician an extremely wide selectionof available voices.

SUMMARY OF THE INVENTION These and other objectives are achieved in aCOM- PUTOR ORGAN Of the type described in the above mentioned U.S. Pat.No. 3,809,786. In such an instrument, musical notes are produced bycomputing in real time the amplitudes X,,(qR) at successive samplepoints gR of a musical waveshape, and converting these amplitudes totones as the computations are carried out. Each sample point amplitudeis computed during a regular time interval t, according to therelationship:

where q is an integer incremented each time interval the value n=l,2,3 Wrepresents the order of the Fourier component being evaluated, and R isa frequency number that establishes the fundamental frequency of thegenerated note. Attack and decay are governed by a time dependent scalefactor 8(1) that defines the amplitude envelope of the produced tone.

The tonal quality or voice of the generated note is established by a setof harmonic coefficients C, that define the relative amplitudes of theconstituent Fourier components. For example, a diapason voice isobtained by using the set A" of harmonic coefficients listed in table Ibelow. A flute voice results when the coeffici ents of set B are used.

TABLE I-continued Set "A" (Diapason) SetB"(FlutcJ Coefl'r (Relative(Decibel [Relative (Decibel cient Amplitude) Equivalent) Amplitude)Fquivalent) C l 42 [l *50 A very economical scheme for generatingtransient voices in a computor organ is based on the observation thatthe transient is usually a flute tone. Reference to Table I shows that aflute voice has single predominant Fourier component. In other words,the flute waveshape is substantially sinusoidal. In set B of Table I thepredominant coefficient is C so that the produced flute voice will be atthe nominal fundamental frequency of the selected note. On the otherhand, if the second order (n=2) harmonic coefficient C were ofrelatively large value, and all other coefficients C and C through Cwere zerovalued, a 4-foot flute tone would be produced at a frequencytwice that of the selected note.

From the foregoing, it is apparent that a flute-like tone can beproduced using only a single harmonic co efficient D where the order nestablishes the footage of the generated tone. In accordance with thepresent invention, a flute-like transient voice is produced by addingthe single coefficient D to the likeordered coefficient C C, in the setused to produee the desired voice. For example, if the set A ofcoefficients from Table I is used to produce a diapason voice, a 2-footflute-like transient can be introduced by simply adding a singlecoefficient D D to the corresponding coefficient C Usually this is doneonly during the attack portion of tone generation. The desired transientvoice is achieved.

FIG. 3 shows appropriate circuitry for producing transient voices in themanner just described. The transient voice may be introduced andterminated abruptly, as described below in connection with FIG. IA, IDand 1C. Alternatively, the magnitude of the coefficient D, may be variedin time to produce gradual introduction and termination of the transientvoice. This is illustrated in FIGS. 1E and IF, described below.

More complex transient voice effects are achieved by providing separatesets of transient harmonic coefficients D, and adding these to thecorresponding harmonic coefficients C, associated with the selectedvoice. Such an implementation is shown in FIG. 4, which implements thefollowing equation 2.

atq l 2 Note that the production of a flute-like transient tone,discussed above, is a special case of equation 2 wherein D,,=D,, is ofsubstantial value and D,.= for all other values of n.

Another aspect of the present invention involves harmonic modulation asa function of time during attack and decay. This is economicallyachieved by limiting which Fourier components are included in thepresent waveshape amplitude computation. At the start of the attack,only higher order components are included. This is achieved cg, bysetting all harmonic coefficients C, to C,, initially to 0. As timepasses during the attack, the value m that specifies the lowest orderFourier component included in the amplitude computation, is reduced. Asa result, Fourier components of lower order gradually are introducedinto the produced tone. Conversely, during decay the value m graduallyis increased. Thus at the beginning of dacay all Fourier components areincluded in the computation whereas later only the Fourier components ofhigher order are included. The circuitry of FIG. 6 implements suchharmonic modulation.

More complex harmonic modulation is achieved by using separate attackand decay scale factor memories for each harmonic coefficient. In otherwords, the waveshape amplitude is computed in accordance with thefollowing relationship:

1r Strl C sin nqR (Eq. 3)

where separate scale factors 8(1), are provided for each Fouriercomponent. FIG. 7 shows an illustrative mechanization of such harmonicmodulation.

As illustrated by Table I above, different voices can be obtained merelyby utilizing different sets of harmonic coefficients C Another aspect ofthe present invention relates to means for providing additional oroptional sets of such coefficients for use by the computor organ. In thetypical embodiment of FIG. 8, extra voices are obtained via an externaldata insertion device such as a card reader, or from storage ofadditional sets of harmonic coefficients in an auxiliary memory.

BRIEF DESCRIPTION OF THE DRAWINGS A detailed description of theinvention will be made with reference to the accompanying drawings,wherein like numerals designate corresponding parts in the severalfigures.

FIGS. 1A through 1F show waveforms associated with transient voicegeneration utilizing the circuitry of FIGS. 2 and 3.

FIG. 2 is an electrical block diagram of a computor organ in which atransient voice is introduced at the beginning of tone production.

FIG. 3 is an electrical block diagram showing a modification of thecomputor organ of FIG. 2 wherein the attack scaling of the generatedtone does not scale the transient voice.

FIG. 4 is an electrical block diagram of circuitry for producing chiffor other selectable transient voice effects in an electronic musicalinstrument.

FIG. 5 is an electrical block diagram of the attackldecay control logicand scale factor memories utilized in the instrument of FIG. 2.

FIG. 6 is an electrical block diagram of circuitry for modulating theharmonic content of a tone produced by a computor organ as a function oftime during attack and decay.

FIG. 7 is an electrical block diagram of circuitry for separatelyscaling the constituent Fourier components of a musical tone produced bya computor organ during attack and decay.

FIG. 8 is an electrical block diagram of circuitry for providingalternative voices in a computor organ.

DESCRIPTION OF THE PREFERRED EMBODIMENTS The following detaileddescription is of the best presently contemplated modes of carrying outthe invention. This description is not to be taken in a limiting sense,but is made merely for the purpose of illustrating the generalprinciples of the invention since the scope of the invention best isdefined by the appended claims.

Operational characteristics attributed to forms of the invention firstdescribed also shall be attributed to forms later described, unless suchcharacteristics obviously are inapplicable or unless specific exceptionis made.

The voicing improvements disclosed herein operate in conjunction withthe basic computor organ 10 of FIG. 2. In this instrument, each time oneof the keyboard switches 11 is depressed, a corresponding tone isproduced via a sound system 12. The voice or tonal quality of theproduced sound is established by a set of harmonic coefficients C storedin a memory 13. In the embodiment of FIG. 2, a sinusoidal or flute-liketransient voice is introduced during the attack by means of additionalcircuitry 14. This circuitry adds the transient coefficient D to thecorresponding harmonic coefficient C C,,- in an adder 15. Accordingly,the system of FIG. 2 implements equation 2 above for the special casewhere all values of D are except for order n=n.

Observe that if the circuitry 14 were omitted, the basic computor organ(FIG. 2) would operate in accordance with equation 1 to produce toneshaving no transient voice. Operation of the instrument It) in this modefirst will be described, since each of the voicing improvementsdisclosed herein operates in conjunction with this basic instrument.

Successive waveshape sample point amplitudes X (qR) are computed atregular time intervals I, in accordance with equation I. In theillustrative embodiment described herein, a maximum of W= l 6 individualFourier components are separately evaluated during correspondingcalculation time intervals 1 through r These time intervals areestablished by a clock 16 that supplies pulses on a line 17 at intervalst to a counter 18 of modulo W=l6. The contents of the counter 18designates the order n of the Fourier component currently beingevaluated. Signals designating the order n are provided on a line 19. Acomputation interval 2, timing pulse is provided on a line 20 byslightly delaying the counter 18 reset pulse (which occurs at time r ina delay circuit 21.

The fundamental frequency of the generated tone is established by afrequency number R accessed from a frequency number memory 23 inresponse to selection ofa keyboard switch 11. At the beginning of eachcomputation interval 2, the frequency number R, provided via a line 24and a gate 25, is added to the previous contents of a note intervaladder 26. Thus the contents of the adder 26, supplied via a line 27,represents the value (qR) designating the waveshape sample pointpresently being evaluated. Preferably, the note interval adder 26 is ofmodulo 2W, where W is the highest order Fourier component evaluated bythe instrument 10. In the embodiment described herein, W=l6, sincesixteen Fourier components are sufficient for most pipe organ tonesynthesis.

Each calculation timing pulse t,.,, is supplied via the line 17 to agate 28. This gate 28 provides the value qR to a harmonic interval adder29 which is cleared at the end of each amplitude computation interval iThus 5 the contents of the harmonic interval adder 29 is incremented bythe value (qR) at each calculation interval r through 1 so that thecontents of the adder 29 represents the quantity (nqR). This value isavailable on a line 30.

An address decoder 31 accesses from a sinusoid table 32 the valuesin(1r/W)nqR corresponding to the argument nqR received via the line 30.The sinusoid table 32 may comprise a read only memory storing values ofsin(1'r/W) d: for 0 s b (W/2) at intervals of D, where D is called theresolution constant of the memory. With this arrangement, the valuesin(1r/W)qR will be supplied on a line 33 during the first calculationinterval r During the next interval 1 the value sin(1r/W)2qR will bepresent on the line 33. Thus in general the value sin(rr/W)nqR will beprovided from the sinusoid table 32 for the particular n'" ordercomponent specified by the contents of the counter 18.

As mentioned earlier, a set of harmonic coefficients C is stored in theharmonic coefficient memory 13. As each sinusoid value is supplied onthe line 33, the harmonic coefficient C for the corresponding n'" ordercomponent is accessed from the memory I3 by a memory address controlcircuit 36 which receives the value n from the line 19. The accessedvalue C is supplied via a line 37, the adder l5 and a line 37a to aharmonic coefficient scaler 38 where it is multipled by the attackldecayamplitude scale factor S(t) present on a line 39. The product S(t)C,,,provided via a line 40, is multiplied by the value sin(1r/W)nqR on theline 33 in a harmonic amplitude multiplier 41. The output of themultiplier 41, corresponding to the value of the Fourier componentpresently being evaluated, is supplied via a line 42 to an accumulator43.

The individually calculated Fourier components are summed in theaccumulator 43. Thus at the end of each computation time interval thecontents of the accumulator 43 represents the waveshape amplitude X (qR)for the current sample point qR. Occurrence of the t, pulse on the line20 transfers the contents of the accumulator 43 via a gate 44 to adigital-to-analog converter 45. The accumulator 43 then is cleared inprepa ration for summing of the Fourier components associated with thenext sample point, computation of which begins immediately.

The digital-to-analog converter 45 supplies to the sound system 12 avoltage corresponding to the waveshape amplitude just computed. Sincethese computations are carried out in real time, the analog voltagesupplied from the converter 45 comprises a musical waveshape having afundamental frequency established by the frequency number R then beingsupplied from the memory 23.

The amplitude scale factors 8(1) are supplied from an attack/decay scalefactor memory 47 that is accessed by an appropriate control circuit 48operating in conjunction with attack/decay control logic 49, all ofwhich are described in detail in conjunction with FIG. 5 below.

Readout of the attack scale factors from the memory 47 is initiated whenany keyboard switch 11 is closed. Such switch closure causes a keydepressed signal to occur on a line 50 to initiate the attack.Successive scale factors S(t) are accessed from the memory 47 at 7 eachfull, half or quarter cycle of the note being generated, in accordancewith the setting of a switch 51.

Since the note interval adder 26 is of modulo 2W, it will reach a countof 32 at the end of each cycle of the selected note. At this time, anoutput will appear on a line 52. Thus with the switch 51 in the positionshown in FIG. 2, a signal will occur on a line 53 at the end of eachfull cycle of note generation. At each half cycle, the note intervaladder 26 will reach a count of 16 or 32. The corresponding outputs areprovided via an OR gate 54 to a terminal 55 of the switch 51. Similarly,quarter-cycle pulses will be provided to an OR gate 56 when the noteinterval adder 26 reaches a count of 8,l6,24 or 32. At each such time, aquarter-cycle signal will be supplied to the terminal 57 of the switch51. Thus, the setting of the switch 51 will determine whether full, halfor quarter cycle pulses are supplied to the line 53, and hence willdetermine how often successive scale factors 8(1) are accessed from thememory 47. The signals on the line 53 also may be used to controltransient voice duration and/or time dependent harmonic modulation asdescribed below.

The circuit 14 of FIG. 2 effectively inserts a transient voice into thetone generated by the instrument [0. This is done by adding a single,transient-related harmonic-coefficient D to the correspondingprincipal-tone-related coefficient C,,=C,, during evaluation of the n=n'order Fourier component. In effect, this causes the addition to theprincipal tone of a sinusoidal or flute-like transient voice having afrequency determined by the order n.

Advantageously, the coefficient D, is a binary number which contains asingle binary 1 bit. The position of this l-bit establishes the relativeamplitude of the transient voice. In the circuit 14, the coefficient D,is loaded into a shift register 59 upon occurrence of the key depressedsignal at the beginning of note production. A switch 60 permits manualselection of the transient voice relative amplitude by controlling theposition of the single l-bit in the coefficient D, For example, with theswitch 60 set as shown in FIG. 2, the single binary l-bit will be loadedinto the second shift register position 59-2. Binary zeros will beloaded into all other positions 59-1 and 59-3 through 59-1'.

The order n' of the transient voice coefficient D, is established by asignal supplied on a line 61. As indicated in the following Table II,the value it establishes the footage of the transient voice. The nsignal may be provided to the line 61 from a manual switch (not shown)so as to allow selection by the musician of the transient voice footage.Alternatively, the input to the line 61 may be hard-wired so that acertain value of n always is provided.

TABLE II Order 11' of Footage of Transient Voice Transient CoefficientDn' Voice n l 8-foot Transient Voice insertion is initiated as soon asany keyboard switch 11 is selected. At that time, the key depressed"signal on the line 50 sets a flip-flop 62 to the I state, therebyenabling an AND gate 63. The

value 11' supplied on the line 61 is compared with the value n presenton the line 19 by a comparator circuit 64. When the Fourier component oforder n=n' is being evaluated, the comparator 64 will provide an outputvia a line 65 and the enabled AND gate 63 to enable a gate 66. As aresult. the transient-related coefficient D, is supplied from the shiftregister 59 via a line 67, the enabled gate 66 and a line 68 to theadder 15 where it is summed with the corresponding harmonic coefficientC, present on the line 37. The combined coefficient (D r +C,,) issupplied via the line 37a to the harmonic coefficient sealer 38. In thismanner, the instrument l0 computes the waveshape sample point amplitudesin accordance with equation 2 above. Transient voice insertion isaccomplished.

The length of time that the transient voice is inserted is establishedby a transient duration counter 69 that is reset by the "key depressedsignal on the line 50. With a switch 70 set to the position shown inFIG. 2, the counter 69 counts timing pulses from a transient durationrate clock 71. When a preset count has been reached, the counter 69provides a signal on a line 72 that resets the flip-flop 62. As aresult, the AND gate 63 is disabled, so that the compare signal from thecomparator 64 can no longer enable the gate 66. This pre vents thecoefficient D, r from reaching the adder 15, so that tone productioncontinues only with the harmonic coefficients C,.. In other words,insertion of the transient voice terminates, and the instrument 10continues note production in accordance with equation 1 above.

The transient voice duration may be related to the number of cycles ofthe principal tone generated by the instrument 10. To accomplish this,the switch 70 is transferred to the contact 70a, so that the quarter,half or full-cycle signals from the line 53 are supplied to thetransient duration counter 69. After a preset number of such signalshave occurred, the counter 69 provides the signal on the line 72 thatterminates transient voice insertion.

FIGS. 1A, 1B and 1C illustrate such transient voice insertion. Thewaveshape 74 of FIG. 1A represents the principal tone generated by thecomputor organ 10 using only the harmonic coefficients C,,. Forsimplicity, this waveshape is shown as a sinusoid, however moretypically it would be a complex waveshape. The inserted transient voiceitself is illustrated by the waveshape 75 of FIG. 1B. This voice isgenerated by a coefficient D having an order n'=3 so that the transientvoice has an effective 2 its footage. The transient voice 75 begins attime T when a keyboard switch 11 is depressed, and ends at a time Testablished by the transient duration counter 69.

The waveshape 76 of FIG. 1C is the actual waveshape generated by theinstrument 10. Prior to the time T,, this waveshape 76 contains thecombined principal tone 74 and transient voice 75. Subsequent to theabrupt termination of the transient voice at time T the producedwaveshape 76 contains only the principal tone 74.

In the waveshape 76, both the principal tone and the transient voicebegin abruptly. However, in practice the attack scale factors 5(1)provided from the memory 47 (FIG. 2) are used in the scaler 38 to scalethe combined harmonic coefficients (C,,+D,," provided on the line 37a.The result is that the combined principal and transient voices graduallyincrease in amplitude during the attack period. This is illustrated bythe waveshape 77 of FIG. 1D, which is the same as waveshape 76, but witha gradually increasing amplitude resultant from scaling by the attackscale factors S(t).

It may be desirable to have the transient voice die out slowly ratherthan to end abruptly as shown in FIG. 18. Such transient decay readilymay be accomplished merely by right shifting the contents of the shiftregister 59 during transient voice insertion. Recall that the register59 contains the coefficient D r and that this coefficient consists of abinary number having a single I- bit. The position of this l-bitestablishes the relative amplitude of the transient voice. Byright-shifting the position of the single l-bit in the register 59, thevalue D r is reduced. Specifically, the value is halved for each rightshift of one position. This results in a corresponding decrease inrelative amplitude of the inserted transient voice.

Right-shifting of the register 59 is accomplished by closing a transientdecay switch 78 to enable an AND gate 79. This permits shift pulses tobe supplied to the register 59 from a transient decay rate clock 80.These pulses may be supplied during the entire transient voice duration,so that the decay begins immediately. Alternatively, the AND gate 79 maybe enabled only during the latter portion of transient voice productionby providing an enable signal on a line 81 from the counter 69 duringthe desired portion of transient production.

The resultant gradual decay of the transient voice is illustrated by thewaveshape 82 of FIG. 1E. Here, transient voice insertion terminates attime T Between the times T, and T the transient voice continues to beinserted, but with decreasing amplitude.

Observe in FIG. 1E that both the transient and principal voices increasein amplitude at the beginning of note production, as established by theattack scale factors 8(2). An alternative arrangement, shown in FIG. 3,permits the transient voice to begin abruptly at full amplitude, whilethe principal tone exhibits the normal attack amplitude characteristics.The resultant waveshape 83 is shown in FIG. 1E. To accomplish this, theharmonic coefficients C, are scaled by the attack/decay scale factorsS(t), but the transient-related coefficient 0,, is not so scaled. Thisis accomplished by supplying the output of the harmonic coefficientmemory 13 directly to the scaler 38, as shown in FIG. 3. The coefficientD r is added to the scaled quotient S(t)C,, present on a line 40d fromthe scaler 38. This is accomplished in an adder 15a that provides theoutput D +(S(t)C,,) on a line 40b to the harmonic amplitude multiplier41. The result is the waveshape shown in FIG. 1F.

In the transient voice insertion circuitry 85 of FIG. 4, a set oftransient-related harmonic coefficients 0,, are contained in theregister positions 86-] through 86-16 of a shift register 86. Eachcoefficient 0,, is added to the corresponding principal voice harmoniccoefficient C in an adder 15' during transient voice insertion. As aresult, the computor organ together with the circuitry 85 generate tonesin accordance with equation 2 above.

The duration of transient voice insertion is established by a counter 69which enables a gate 87 throughout the entire transient voice period.When so enabled, the gate 87 supplies the harmonic coefficient D,contained in the first shift register position 86-1 via a line 88 to theadder The coefficients 0,, are recirculated through the register 86 inunison with the clock pulses 1 so-that the first register position 86-1always contains the harmonic coefficient D of order n corresponding tothe coefficient C simultaneously provided on the line 37. Therecirculation is implemented by feeding the output of the first registerposition 86-1 back via the line 88, an enabled AND gate 89 and a line 90to the last register position 86-16. Right shifting of the register 86is enabled by t clock pulses on the line 17.

The circuitry just described facilitates insertion of a transient voiceof any tonal quality. Like the principal voice, the transient voice maycontain up to W Fourier components having independent relativeamplitudes established by the set of coefficients D stored in the shiftregister 86. Some or all of these coefficients may be zero-valued. Forexample, a chiff effect is achieved by using all zero-valuedcoefficients D, except for D or D,,. The result will be chiff-likeaugmentation of the third or fifth harmonic of the principal voice.

Unusual transient voice effects can be achieved with the circuit bychanging the contents of the shift register 86 during transient voiceproduction. To this end, different sets of transient harmoniccoefficients are maintained in respective storage devices 92 and 93. Atcertain times during transient voice production, the set of coefficientscontained in the memory 92 or 93 is transferred into the shift register86 in place of the previous contents thereof.

For example, after a certain number of cycles of the principal tone havebeen generated, the transient duration counter 69' may provide a signalon a line 94 which causes the harmonic coefficients from the storagedevice 92 to be transferred to the shift register 86. The signal on theline 94, supplied via an OR gate 95, sets a flip-flop 96 to the 1 state.This disables the AND gate 89 so that the coefficients previously in theshift register 86 are not recirculated. A storage access control 97 isenabled to read out from the storage device 92 the coefficient D, oforder n specified by the signal on the line 19. This accessedcoefficient is supplied via a line 98, and AND gate 99 enabled by thesignal on the line 94, and the line to the shift register position86-16. This transfer operation continues until all 16 coefficients D,from the storage device 92 have been transferred to the shift register86.

A counter 100 determines when the transfer has been completed. To thisend, an AND gate 101 enabled by the 1 output of flip-flop 96, gatestiming pulses I from the line 17 to the counter 100. When a count ofW=l6 has been reached, corresponding with transfer of all l6coefficients to the register 86, the counter 100 provides an output on aline 102 that resets the flip-flop 96. As a result, the transfer isterminated, and the AND gate 89 again is enabled to permit continuedrecirculation of the shift register 86.

Later in the transient voice period, another output is obtained from thecounter 69' on a line 103. This signal initiates transfer of the set ofharmonic coefficients from the second storage device 93 via an AND gate104 to the shift register 86. In this manner, the sets of harmoniccoefficients used to generate the transient voice are programmaticallyaltered as a function of time. Very unusual transient voice effects canbe achieved.

Details of the attack/decay scale factor memory 47, the memory accesscontrol 48 and the attack/decay control logic 49 are shown in FIG. 5.

During the attack and sustain periods, the scale factors S(t) areprovided from a memory 470 that has a plurality of storage locations47-1 through 47-p each of which contains a separate value S(l). Thesestored scale factors are accessed successively under the control of aparallel load shift register 106 having a corresponding plurality ofpositions 106-1 through 106-p. Only one of these positions contains abinary 1 bit. The storage location in the memory 47a corresponding tothe register position containing the I bit provides the scale factorS(!) to a line 107 and thence via an enabled AND gate 108 and an OR gate109 to the line 39.

Such readout of the attack-sustain scale factor memory 47a is initiatedeach time that a keyboard switch 11 is closed. For example, if the noteC is selected by closing the corresponding switch 110, a signal issupplied via a line 111 and an OR gate 112 to a one-shot multivibrator113. This produces the "key depressed" pulse on the line 50 thatinitiates readout of the memory 470.

The key depressed" pulse is provided to the "load" input of the shiftregister 106 to cause entry ofa binary I bit into the position 106-1,and to cause binary bits to be entered into all other positions. The keydepressed" pulse also sets a flip-flop 114 to the I state so as toenable an AND gate 115. Accordingly, the quarter, half or full cyclepulses on the line 53 are fed via the AND gate 115 to the shift input ofthe register 106. As a result, the single binary 1 bit contained in thatregister is advanced from location to location as each pulse occurs onthe line 53. Successive scale factors S(t) thus are accessed from thememory 470 at a rate proportional to generation of successive cycles ofthe selected principal tone.

The end of attack occurs when the single I bit in the register 106reaches the position 106-p. At that time, a signal is provided via aline 116 to the reset (R) input of the flip-flop 114. This resets theflip-flop 114 to the 0 state, thereby disabling the AND gate 115 so thatno more shift pulses are provided to the register 106.

The final attack scale factor S(l) contained in the memory location106-p continues to be supplied via the line 39 until the selectedkeyboard switch 11 is released. That is, the scale factor in the storagelocation 106-p establishes the envelope amplitude of the produced toneduring the sustain period.

Decay begins when the selected keyboard switch 11 is released. Tofacilitate continued tone production during the decay period, thefrequency number memory 23 is accessed in response to a set offlip-flops 118 each associated with a corresponding keyboard switch 11.Thus the switches 110, 119 and 120 for the notes C D, and C areconnected to the set (S) inputs of respective flip-flops 118-1, 118-qand 118-r.

Thus, e.g., when the switch 110 is closed, the flip-flop 118-! is set,and a signal is provided via a line 121 to cause access from the memory23 of the frequency number R associated with the note C,. When thekeyboard switch 110 is released, the flip-flop 118-! is not immediatelyreset. As a result, the signal on the line 121 remains high so that theselected frequency number R continues to be accessed from the memory 23during the decay period. However, opening of the switch causes theoutput of the OR gate 112 to go low. As a result, an inverter 122provides a high output that triggers a one-shot multivibrator 123. Thisin turn produces a start of decay" signal on a line 124. This signalcauses amplitude scale factors S(t) to be supplied to the line 39 fromthe decay scale factor memory 476.

To this end, the start of decay signal sets a flip-flop 125 to the 1state, This disables the AND gate 108 to prevent scale factors from thememory 47a from reaching the line 39. The 1 output from the flip-flop125 is supplied via a line 126 to enable an AND gate 127 to open a pathfor scale factors S(t) from the decay scale factor memory 47b via the ORgate 109 to the line 39.

The "start of decay" signal on the line 124 also is fed to the load"input of a parallel load shift register 128 that is used to access thedecay scale factor memory 471). Like the register 106, the shiftregister 128 includes a plurality of locations l28-l through 128-kcorresponding respectively to the storage locations 129-! through 129-kin the memory 47b. At the start of decay, a single binary I bit isloaded into the shift register position 128-1. The corresponding memoryposition 129-! preferably contains a scale factor 8(1) having a valueequal to or very close to that stored in the attacksustain scale factormemory position 47-p.

The 1 output from the flip-flop 125 also enables an AND gate 130 whichfeeds the quarter, half or whole cycle pulses from the line 53 to theshift" input of the register 128. Accordingly, decay scale factors 8(2)are successively accessed from the memory 47b as the single I bit isshifted through the register 128. This results in decreasing amplitudeof the generated principal tone.

The decay ends when the single 1 bit reaches the final register location128-k. At this time, an end of decay" signal occurs on a line 131. Thissignal resets all of the flip-flops 118, to terminate access of theselected frequency number from the memory 23, and hence to terminatenote production. Further, the end of decay" signal resets the flip-flop125 to the 0 state. This disables the AND gate 127 and enables the ANDgate 108 to insure that attack scale factors from the memory 47a will besupplied to the line 39 when the next keyboard switch 11 is depressed.

Harmonic modulation as a function of time during attack and decay isimplemented in a computor organ 10 by the circuitry of FIG. 6. At thebeginning of attack, only higher order Fourier components are includedin the waveshape amplitude computation. As the attack progresses,additional lower order Fourier components are added to each computation,until finally all W Fourier components are included in the evaluation.This is illustrated by the following Table [11, wherein a zero indicatesthat the corresponding Fourier component is omitted from the waveshapeamplitude computation, and a 1 indicates that the component is included.

TABLE [11 Quarter Cycles of Order I: of Fourier Component -I GeneratedTone l 2 3 4 5 6 7 8 9 10 ll l2 l3 l4 l5 16 START OF ATTACK 0 0 0 0 0 O0 O 0 0 0 0 TABLE Ill-continued Quarter Generated Tone l 6 7 8 9 ll 1213 l4 l5 l6 l I 1 I l I l l l l I l l l l 1 l I I to a gate 140. [f theregister position 136-1 contains a binary one, the resultant signal onthe line 139 enables the gate 140 to supply the harmonic coefficient C,present on the line 37 via a line 37' to the harmonic coefficient sealer38. This component is included in the waveshape amplitude calculation.On the other hand, if the register position 136-1 contains a binary 0,no signal is supplied on the line 139 and the gate 140 is disabled. Thisprevents the corresponding harmonic coefficient C from reaching thescaler 38, thereby effectively deleting the corresponding Fouriercomponent TABLE IV Quarter Cycles of Order n of Fourier Component -1Generated Tone I 2 3 4 5 6 7 B 9 I0 I I I2 I 3 l4 I5 16 START OF DECAY Il I I l I l I I l I I I I l I I I I l I I 0 0 0 0 0 0 0 0 0 0 0 2 I I lI I 0 O 0 0 0 0 O 0 0 0 0 3 I I l I 0 0 0 0 0 0 0 0 0 0 0 0 4 I I I I 0O 0 0 0 0 0 I) 0 0 0 0 5 l I I 0 O 0 0 O 0 0 0 0 0 0 0 O 6 l I I 0 0 0 0O 0 0 O 0 0 0 0 0 7 I 1 0 0 0 0 0 0 0 0 0 0 0 O 0 0 8 l l 0 0 0 0 0 0 0O 0 0 0 0 O O 9 I O 0 I] 0 0 0 O 0 0 I) 0 0 I] 0 0 IO 1 O 0 0 0 0 0 O I)0 O 0 0 0 0 0 In the embodiment of Table IV, during the first quartercycle of the decay, only Fourier components of order n=5 or less areincluded in the amplitude computation. All higher order Fouriercomponents are omitted. During later quarter cycles of the decay,additional Fourier components are deleted, until, at the tenth quartercycle, only the fundamental component (n=1 is utilized.

The scheme illustrated by the Tables 11] and IV is implemented by thecircuitry 135 (FIG. 6). Specifically, a shift register 136 contains asingle 16-bit binary number, each bit of which designates whether or notthe Fourier component of corresponding order is to be included in theamplitude computation. For example, at the start of attack, the shiftregister 136 will contain the number (000001 1111111111). Thiscorresponds to the first line of Table 111 above. Each bit is containedin a respective shift register position 136-1 through 136-16 associatedwith a respective value of n.

The contents of the shift register 136 is left-shifted by one positionat each calculation time interval at The contents of the first registerposition 136-1 is provided via a line 137, an enabled AND gate 138 and aline 139 from the amplitude computation.

The shift register 136 is loaded at the beginning of each computationinterval upon occurrence of the r, pulse on the line 20. The numberloaded into the register 136 is established by a set of flip-flops 142cooperating with an attack/decay cycle counter 143. The counter 143 isreset at the beginning of attack by occurrence of the key depressed"signal on the line 50. This signal, supplied via an OR gate 144 and aline 145, resets both the counter 143 and all of the flip-flops 142.

Upon occurrence of the first full, half or quarter cycle pulse on theline 53, the counter 143 registers a count of 1. The resultant output ona line 146 sets a first flip-flop 142-1 to the I state. This enables agate 147 to supply binary ls to all of the shift register positions136-6 through 136-16. The remainder of the flipflops 142-2 through 142-6remain in the 0 state. As a result, binary 0's are entered into each ofthe shift register positions 136-1 through 136-5. In other words, thecontents of the shift register 136 now coincides with the first line ofTable III. Shifting of the register 136 and readout onto the line 139proceeds as described above, with the result that only Fouriercomponents of order n=6 or greater are included in the waveshapeamplitude calculation.

As additional quarter cycles of the tone are generated, correspondingpulses occur on the line 53. When the counter 143 reaches a count ofthree, the flip-flop [42-2 is set. Thus, upon occurrence of the next ipulse on the line 20, binary l's will be entered into shift registerpositions 136-5 through 136-16. The contents of the register 136 nowwill correspond to that of the third line of Table Ill. Accordingly,Fourier components of order n=5 or greater will be included in theamplitude computation.

Operation in this manner continues, with the flipflops 142-3 through142-6 being set respectively when the counter 143 reaches a count of5,7,9 and 1]. Thereafter, binary ls are loaded into all positions of theshift register 136 at each occurrence of the pulse t All W Fouriercomponents are included in the amplitude computation.

A similar operation takes place during decay. The start of decay" pulse,supplied via the line 124, the OR gate 144 and the line 145, resets allof the flip-flops 142 and the counter 143. In addition, the start ofdecay" pulse sets a flip-flop 149 to the 1 state. This disables the ANDgate 138 and enables another AND gate 150. Now the signal from the shiftregister position 136-] is inverted by an inverter 151. The invertedsignal is supplied via the enabled AND gate 150 and the line 139 to thegate 140. As a result of the inversion, occurrence of a binary l-bit inthe register position 136-1 will cause the gate 140 to be inhibited,thereby deleting the corresponding Fourier component from the waveshapeamplitude computation. Conversely, ifa binary zero is present in theposition 136-1, the gate 140 will be enabled and the correspondingharmonic coefficient C, will be supplied to the scaler 38.

During decay, the shift register 136 is loaded in exactly the same wayas during the attack. Thus, upon occurrence of the first pulse on theline 53 following the "start of decay", the counter 143 assumes a countof one, and the flip-flop 142-1 is set. The binary number (000001 1 l Il l l l l l l) is loaded into the shift register 136. Now, because ofthe inversion operation just described, the contents of the register 136cause the first five Fourier components to be included in the waveshapecalculation. However, all components of order n=6 or greater are deletedfrom the computation. That is, the circuitry accomplishes the harmonicmodulation indicated by line one of Table IV above. As the decayprogresses, fewer and fewer components are included in the calculation,until subsequent to the ninth pulse on the line 53, only the fundamental(n=l component is utilized. At count 11 the flip-flop 142-6 is not set,since an AND gate 152 is disabled during decay. When the decayterminates, the "end of decay" signal on the line 131 resets theflip-flop 149. This disables the AND gate 150 and enables the AND gates138 and 152 in preparation for production of the next note.

A limitation of the harmonic modulation system just described ariseswhen the desired tone has few higher harmonics. For example, supposethat an 8-foot flute tone is played. This voice consists primarily of asingle sinusoid at the fundamental frequency, hence only the Fouriercomponent of n=l is of substantial value. Accordingly, if the attackscheme illustrated in Table III is used, little or no sound will beproduced until the eleventh quarter cycle. At that time, generation ofthe fun- 16 damental will begin abruptly rather than gradually, Anobjectionable keying click also might resultv Similarly, ifa l-footsinusoidal or flute-like tone were being played, a gradual attack wouldbe achieved, but an abrupt decay would result, This is evident fromTable IV, which shows that the l-foot signal (corresponding to aharmonic order n=6) will end abruptly after the second quarter cycle ofthe decay.

These limitations are overcome by using the additional circuitry 154shown in phantom in FIG. 6. A set of switches are associated withflute-like or similar sinusoidal voices. If an 8-foot sinusoidal stopswitch 155a is closed, the counter 143 is preset to a count of eleven.As a result, the attack proceeds immediately from the eleventh steplisted in Table III above. Since this causes the shift register 136 tohave all 1 s to be entered therein, all harmonics will be included inthe waveshape amplitude computation immediately from the beginning ofthe attack. Since the selected 8-foot sinusoidal tone consists primarilyor entirely of a single Fourier component of order n=l, this componentwill be included in the amplitude computation from the beginning of theattack. The tone will come on gradually, exactly as desired.

During decay, the counter 143 is disabled whenever any sinusoidal voiceis selected. As a result, all Os are loaded into the shift register 136,and all harmonic coefficients C, are supplied to the sealer 38. However,since only one of these coefficients C,, is of substantial amplitude,the tone continues to be produced throughout the decay, with theenvelope amplitude controlled by the decay scale factors 8(2) suppliedon the line 39. There is no abrupt termination of the decay.

To disable the counter 143 during decay, closure of any switch 155provides a signal via an OR gate 157 to an AND gate 158. During decay,the 1 output of the flip-flop 149 enables the AND gate 158, so that asignal is supplied via a line 159 to the disable" terminal of thecounter 143.

Another technique for modulating the harmonic content of the generatedtone as a function of time during attack and decay is shown in FIG. 7.In this embodiment, the attack and decay scale factor memories 47a, 47bof FIG. 5 are not employed with the computor organ 10. Rather, separateattack/decay scale factors S(t),, are provided from a set of memories160 for each of the constituent Fourier components. For example, duringevaluation of the fundamental (n=l) Fourier component, the harmoniccoefficient C present on the line 37 is scaled by the scale factor 3(1)supplied from the memory 160-1 via an AND gate 161-] enabled by the n=lsignal from the counter 18. Similarly, the remaining Fourier componentsof order n=2 through n=16 are scaled respectively by separate scalefactors provided from the memories 160-2 through 160-16 and theassociated AND gates 161-2 through 161-16.

Each of the memories 160 is accessed by an associated memory accesscontrol 162-1 through 162-16. These control circuits 162 all areresponsive to the contents of an attack/decay cycle counter 163 whichcounts the quarter, half or full cycle pulses received on the line 53from the note interval adder 26.1n this manner, the scale factors 5(1),,are updated selectively as time progresses during the attack and decay.This updating need not be tied to the number of cycles of the generatedtone. Alternatively, the counter 163 could count pulses from an optionalclock 164 shown in FIG. 7. This is accomplished when a switch 167,normally set to the position 167a, is transferred to the position 167b.

The counter 163 is reset at the beginning of both attack and decay. Thisis accomplished by providing the key depressed and start of decaysignals via an OR gate 165 to the reset terminal of the counter 163. Aflip-flop 166 indicates to the control circuits 162 whether attack (A)or decay (D) is in progress. The flip-flop 166 is set by the start ofdecay" signal on the line 124. it is reset by a end of decay signalobtained from the counter 163 when a preset count is reached. This endof decay signal also is supplied via a line 131' back to theattack/decay control logic 49 (FIGS. 3 and S) to cause resetting of theflip-flops 118. The flip-flop 166 is set to the 1 state only duringdecay, and remains in the state during attack and sustain. Thearrangement of FIG. 7 provides complete flexibility for modulation as afunction of time of the harmonic content of the generated tone.

Provision of extra voices for the computor organ 10 is facilitated bythe circuitry 170 of FIG. 8. Typically, the instrument 10 will beprovided at the factory with not one, but a set of harmonic coefficientmemories 13, 13 and associated access controls 36, 36'. Each of thememories 13, 13' will store a set of harmonic coefficients C, associatedwith a respective voice. For example, the memory 13 may include thecoefficients of set A of Table I, while the memory 13 may include theset B of Table I. Accordingly, if the stop tab switch 171A is closed adiapason tone will be produced; if the stop 1718 is closed, a flute tonewill result.

The number of such memories 13, 13' contained in the instrument is ofcourse an economic factor. Generally, the instrument manufacturer willprovide sufficient voices to satisfy the average user. However, greaterflexibility of voicing may be desired by the musician. For example, theinstrument as sold may contain voices preferred for entertainmentpurposes. A musician, however, may desire voices that more accuratelysimulate pipe organ sounds.

Voicing at the selection of the musician advantageously is accomplishedby providing the instrument It) with an external data insertion device172 that is used to provide additional sets of harmonic coefficients C,to the instrument. For example, the device 172 may be a punched cardreader, a punched tape reader, an optical reader that senses markedcards or tape, a magnetic card or magnetic tape reader, a diodepegboard, or merely a set of switches.

The optional voice is selected by turning a switch 173 to connect with aterminal 173a. This connects a random access scratch pad" memory 174 viaa line 175, the switch 173 and a line 37b to the scaler 38. As a result,during the waveshape amplitude computations, the appropriatecoefficients C, are supplied fromthe memory 174 under the direction of amemory access control 176 that receives the present value n from theline 19.

The optional voice harmonic coefficients are entered into the randomaccess memory 174 from the insertion device 172 when a switch 177 is inthe position shown in FIG. 8. For example, the device 172 may be apunched card reader. The instrument manufacturer may provide to a user adeck of punched cards, each of which contains in coded form a set ofharmonic coefficients associated with a different voice. The musicianwill then select the desired voice, and feed the card into the device172. The coefficients will be transferred into 18 the random accessmemory 174, from which they will be accessed as required during the realtime waveshape synthesis.

As an alternative, the instrument may be provided with a relativelylarge, read only memory 178 that contains many sets of harmoniccoefficients associated with different voices. The switch 177 then maybe used to select which of these stored extra voices is to betransferred into the random access memory 174 for utilization by thecomputor organ 10.

For further flexibility, voices may be combined. Thus, e.g., if theswitch 173 is set to the position 173b, the harmonic coefficients storedin the random access memory 174 will be combined with those providedfrom the selected memory 13, 13'. The combined coefficients, summed byan adder 179, are provided to the scaler 38 so that the instrument 10will produce notes having the combined tonal characteristics of two ormore separate voices.

The various components of the musical instrument disclosed herein areconventional circuits well known in the digital computor art. Asindicated by the following Table V, many of these items are availablecommercially as integrated circuit components.

TABLE V Conventional Integrated 512 words of S-bits [p.l4l88] programmedto store sin values May be implemented as shown in application sheet SIGcatalog. p.28 using SIG 8202 buffer registers and 8260 arithmeticelement Also can be implemented using SIG 8243 scaler [p.65]

Same as harmonic amplitude multiplier 41 SIG 8223 read-only memory whichincludes address control circuitry Harmonic Amplitude (a) Multiplier 41Harmonic coefficient sealer 38 Harmonic coefficient storage 92 andstorage access control 97 TI Texas lmtrucment Co. (Page references areto the Tl integrated Circuits Catalog for Design Engineers, FirstEdition. January, 1972] SIG Sugnetics. Sun nyvale, California [Pagereferences are to the SIG Digital 8000 Series TTL/MSl catalog, copyrightl97l I Flores, lvan Computer Logic" Prentice-Hall. 1960 Intending toclaim all novel, useful and an obvious features shown or described, theapplicant claims:

1. In a musical instrument of the type including generation means forcomputing in real time the amplitudes at successive sample points of amusical waveshape, and a converter for converting said waveshapeamplitudes to musical signals as the computations are carried out, saidgeneration means including circuitry for individually calculating theconstituent Fourier components of that musical waveshape and anaccumulator for summing these Fourier components to obtain eachwaveshape amplitude, the relative amplitudes of said Fourier componentswith respect to each other being established by a set of harmoniccoefficients, the

19 improvement Comprising;

means for adding to one of said harmonic coefficients a single binaryword consisting of all binary s and a single binary lbit to produce atransient voice having a relative amplitude established by the positionof said single l-bit within said word, said transient voice having asubstantially sinusoidal waveshape.

2. In a musical instrument of the type including generation means forcomputing in real time the amplitudes at successive sample points ofthat waveshape, and a converter for converting said waveshape amplitudesto a musical tone as the computations are carried out, said generationmeans including circuitry for individually calculating the constituentFourier components of that musical waveshape, and an accumulator forsumming these Fourier components to obtain each waveshape amplitude. therelative amplitudes of said Fourier components with respect to eachother, and hence the voice of the produced musical tone, beingestablished by a set of harmonic coefficients, said instrument beingprovided with several such sets of harmonic coefficients and with stoptab switches to permit selection of which of such provided sets isutilized by said generation means, the improvement for providingadditional voices to said instrument comprising:

storage means within said instrument for storing an optionally insertedset of harmonic coefficients,

a switch for connecting said generation means to utilize the harmoniccoefficients from said storage means when said switch is in one positionand for connecting said generation means to utilize a set of harmoniccoefficients provided in the instrument when said switch is in anotherposition, and

an external data insertion device for entering said optional set ofharmonic coefficients into said storage means.

3. In a musical instrument of the type including generation means forsynthesizing a musical waveshape by computing in real time theamplitudes at successive sample points of that waveshape, and aconverter for converting said waveshape amplitudes to musical signals asthe computations are carried out, said generation means including firstcircuitry for individually calculating the constituent Fouriercomponents of that musical waveshape, and an accumulator for summingthese Fourier components to obtain each waveshape amplitude the relativeamplitudes of said Fourier components with respect to each other beingestablished by a set of harmonic coefficients utilized by said firstcircuitry, each harmonic coefficient having the same order as thecorresponding Fourier component, the improvement for dynamicallymodifying the voice of the produced musical signals, comprising:

storage means for storing voice modification data each associated with aFourier component of corresponding order, each such voice modificationdata designating the extent to which the relative amplitude of thecorresponding Fourier component should be altered,

access control means for supplying each voice modification data fromsaid storage means in unison with calculation of the Fourier componentof corresponding order, and

modification means for modifying the harmonic coefficient ofcorresponding order in accordance with said supplied voice modificationdata, the modified harmonic coefficients being utilized by 20 saidgeneration means to establish the relative amplitude of thecorresponding Fourier component.

4. A musical instrument according to claim 3 wherein said voicemodification comprises addition of a transient voice, and wherein;

said storage means comprises a register containing a single transientvoice related harmonic coefficient of a specified order, wherein saidaccess control means comprises a comparator for comparing the order ofthe Fourier component presently being calculated with the order of saidsingle transient voice related coefficient, and gate means for supplyingsaid transient voice related coefficient from said register to saidmodification means when said comparator detects identity between thecompared orders, and wherein said modification means comprises an adderfor adding said transient voice related coefficient to the harmoniccoefficient of corresponding order.

5. A musical instrument according to claim 4 wherein said transientvoice related coefficient consists of a binary word having a singlebinary l bit, the position of said l-bit in said word establishing therelative amplitude of the transient voice, further comprising:

transient voice amplitude control means for altering the position ofsaid single l-bit in said register to control the relative amplitude ofsaid transient voice.

6. A musical instrument according to claim 5 wherein said registercomprisies a shift register, and wherein amplitude control meanscomprises;

shift means for shifting the contents of said register at controlledtime intervals.

7. A musical instrument according to claim 3 wherein said voicemodification comprises addition of a transient voice, wherein saidstorage means contains a set of transient voice related harmoniccoefficients of different order, and wherein said modification meanscomprises an adder for adding each supplied transient voice relatedcoefficient to the harmonic coefficient of corresponding order.

8. A musical instrument according to claim 7 wherein said transientvoice produces a chiff effect, and wherein the only transient voicerelated harmonic coefficient of non-negligible value in said set is thatcoefficient associated with the Fourier component contributing a thirdor fifth harmonic to said musical waveshape.

9. A musical instrument according to claim 7 together with;

means for altering the values of the transient voice related harmoniccoefficients contained in said storage means at controlled timeintervals.

10. A musical instrument according to claim 3 wherein said voicemodification comprises modification of the harmonic content of saidmusical signals, wherein:

said storage means comprises a shift register storing a set of binarybits each associated with a particular Fourier component order, thevalue of each bit designating whether or not the correspondidng Fouriercomponent is to be included in the waveshape amplitude summation, andwherein said modification means comprises a gate for enabling theassociated harmonic coefficient to be utilized by said generation meansif the corre- 21 sponding bit is of one binary value, and for providinga zero-valued harmonic coefficient to said generation means if thecorresponding bit is of the other binary value. 11. A musical instrumentaccording to claim further comprising;

means for loading different sets of binary bits into said shift registerat controlled time intervals, so that during attack the value ri isdecreased progressively with time, where ri is the lowest Fouriercomponent order included in the waveshape amplitude summation duringattack, and so that during decay the value ri is increased progressivelywith time, where n is the highest Fourier component order included inthe summation dur ing decay. 12. A musical instrument according to claim3 wherein said voice modification comprises modulation of the harmoniccontent of said musical signals, wherein said storage means comprises aplurality of memories each containing a set of attack/decay amplitudescale factors associated with a respective Fourier component order,wherein said access control means is time controlled to access differentscale factors from said memories at different times during waveshapegeneration. and wherein said modification means comprises a scaler formultiplying each harmonic coefficient by the scale factor currentlyaccessed from the memory that stores factors of corresponding order.

13. A musical instrument according to claim 3 together with an externaldata insertion device operatively connected to said first circuitry forproviding said set of harmonic coefficients to said musical instrument,said provided harmonic coefficients being utilized by said generationmeans to establish the tonal quality of the generated musical signals.

14. In a musical instrument of the type having:

first means for computing the Fourier components of a periodic complexwaveshape at successive sample points, said Fourier components beingcomputed separately for each sample point, said computations occurringat a clock rate independent of the period of said waveshape, thecomputed Fourier components having different respective orders n betweena minimum order n and a maximum order ri accumulator means for addingthe component values calculated by said first means to obtain thewaveshape amplitude at said each sample point, and means for providingmusical notes from the waveshape amplitudes obtained in said accumulatormeans, and wherein said first means comprises: note selection meansincluding keyboard switches for selecting a frequency numberestablishing the separation between successive sample points, saidnumber thereby establishing the period of the resultant musical note,note interval adder, operative during each successive amplitudecomputation, to add said selected number of the sum previously containedin said note interval adder, the resultant contents of said noteinterval adder representing the sample point for which said waveshapeamplitude is computed,

means for obtaining a trigonometric value, the argument of saidtrigonometric value being the product of the said sample pointdesignated by the contents of said note interval adder times the orderof the Fourier component presently being calculated,

a harmonic coefficient memory storing a set of harmonic coefficientvalues designating the relatiive amplitude of each constituent Fouriercomponent ofa principal tone with respect to the amplitudes of the otherconstituent Fourier components of that tone, and

a multiplier for multiplying each obtained trigonometric value by themodified harmonic coefficient of order corresponding to that of theFourier component presently being calculated the products of suchmultiplication being the calculated Fourier component values which areadded by said accumulator means to obtain the sample point amplitudes,

the improvement for modifying the tonal quality of the provided musicalnotes during portions of note production, comprising;

attack and decay signal means, responsive to depression and release ofany keyboard switch, for providing respective start of attack and startof decay signals, and

modification means for modifying the harmonic coefficients accessed fromsaid harmonic coefficient memory as a function of time during the attackor decay periods initiated respectively by said start of attack andstart of decay signals, the resultant modified harmonic coefficientsbeing supplied to said multiplier.

15. A musical instrument according to claim 14 wherein said tonalquality is modified by the addition to said principal tone of atransient voice, said modification means comprising:

a storage device containing at least one transientvoice-related harmoniccoefficient, and

an adder for adding each transient-voice-related harmonic coefficient tothe principal-tone-related harmonic coefficient of corresponding orderto obtain a modified harmonic coefficient that is utilized by saidmultiplier during calculation of the Fourier component value ofcorresponding order.

16. A musical instrument according to claim 15 together with;

a transient duration counter, responsive to the contents of said noteinterval adder, for counting the number of fractional cycles of theprovided musical note that have been generated since occurrence of saidstart of attack signal, and

means for changing the values of the transient-voicerelated harmoniccoefficients in said storage device in response to the count of saidtransient duration counter.

17. A musical instrument according to claim 16 wherein said storagedevice is a register storing a single transient-voice-related harmoniccoefficient that is added to the principal-voice-related harmoniccoefficient of corresponding order for a period of time established bysaid transient duration counter, resulting in the production ofatransient voice of substantially sinusoidal waveshape.

18. A musical instrument according to claim 17 wherein said singletransient-voice-related harmonic coefficient consists of a binary numberhaving a single 23 binary I bit. together with clock means for shiftingthe position of said single 1 bit in said number, and hence changing therelative amplitude of the transient voice, as a function of time,

19. A musical instrument according to claim together with,

an attack scale factor memory containing a set of attack scale factorsthat establish the amplitude envelope of the generated principal toneduring at tack, attack memory access control circuitry, initiated bysaid start of attack signal and responsive to the number of cycles ofthe generated tone, for access' ing successive attack scale factors fromsaid scale factor memory, and a scaler for scaling the modified harmoniccoefficients by the scale factor value currently accessed by saidcontrol circuitry prior to utilization of said modified harmoniccoefficient by said multiplier. 20. A musical instrument according toclaim 19 wherein the summed transient-and principal-voicerelatedharmonic coefficients from said adder are scaled by said sealer, so thatthe combined principal tone and transient voice both have an envelopeestablished by said stored attack scale factors.

21. A musical instrument according to claim 19 wherein only saidprincipal-voice-related harmonic coefficient is scaled by said scalerprior to addition to said transient-voice-related harmonic coefficientin said adder, so that only the principal tone but not the transientvoice has an envelope established by said stored attack scale factors.

22. A musical instrument according to claim 14 wherein said tonalquality is modified by selectively, programmatically deleting certainFourier components from each waveshape amplitude computation duringattack and decay, and wherein said modification means comprises:

a storage device containing a single binary word having one binary digitassociated with each Fourier component that can be included in eachwaveshape amplitude computation,

a gate, operative as each harmonic coefficient is accessed from saidharmonic coefficient memory, for permitting said accessed harmoniccoefficient to be utilized by said multiplier if the associated binarydigit is of one binary value and for providing a zerovalued harmoniccoefficient to said multiplier if the 24 associated binary digit is ofthe other binary value, and

time controlled means, initiated by said start of attack or start ofdecay signals, for selectively altering said single binary word atcertain time intervals during attack and/or decay,

23. A musical instrument according to claim 22 wherein:

said storage device comprises a shift register that is shifted in unisonwith the accessing of said harmonic coefficient memory, the contents ofone position of said shift register being used to control the enablingof said gate, and wherein said time controlled means comprises acounter, reset by said start of attack and start of decay signals andresponsive to the contents of said note in terval adder, that counts thenumber of cycles of fractional cycles of the principal tone that havebeen generated since the start of attack or decay, and load circuitryfor entering different binary words into said shift register when thecounter reaches certain preset count values.

24. A musical instrument according to claim 23 wherein said loadcircuitry enters data into said shift register that cause the value ofthe minimum order ri to be decreased progressively during attack, andthat cause the value of the maximum order ri to be decreasedprogressively during decay.

25. A musical instrument according to claim 24 further comprisingcircuitry for preventing such alteration of constituent Fouriercomponent minimum and maximum order when a principal tone having asubstantially sinusoidal waveshape is being generated.

26. A musical instrument according to claim 14 wherein said modificationmeans comprises;

separate attack/decay scale factor memories each containing a set ofattack/decay amplitude scale factors associated with a respectiveFourier component order,

time dependent access control means, initiated by said start of attackand start of decay signals, for accessing different scale factors fromeach attackldecay scale factor memory at different times during attackand decay, and

a harmonic coefficient scaler for multiplying, each harmonic coefficientaccessed from said harmonic coefficient memory by the currently accessedattack/decay scale factor of corresponding order,

1. In a musical instrument of the type including generation means forcomputing in real time the amplitudes at successive sample points of amusical waveshape, and a converter for converting said waveshapeamplitudes to musical signals as the computations are carried out, saidgeneration means including circuitry for individually calculating theconstituent Fourier components of that musical waveshape and anaccumulator for summing these Fourier components to obtain eachwaveshape amplitude, the relative amplitudes of said Fourier componentswith respect to each other being established by a set of harmoniccoefficients, the improvement comprising; means for adding to one ofsaid harmonic coefficients a single binary word consisting of all binary0''s and a single binary 1bit to produce a transient voice having arelative amplitude established by the position of said single 1-bitwithin said word, said transient voice having a substantially sinusoidalwaveshape.
 2. In a musical instrument of the type including generationmeans for computing in real time the amplitudes at successive samplepoints of that waveshape, and a converter for converting said waveshapeamplitudes to a musical tone as the computations are carried out, saidgeneration means including circuitry for individually calculating theconstituent Fourier components of that musical waveshape, and anaccumulator for summing these Fourier components to obtain eachwaveshape amplitude, the relative amplitudes of said Fourier componentswith respect to each other, and hence the voice of the produced musicaltone, being established by a set of harmonic coefficients, saidinstrument being provided with several such sets of harmoniccoefficients and with stop tab switches to permit selection of which ofsuch provided sets is utilized by said generation means, the improvementfor providing additional voices to said instrument comprising: storagemeans within said instrument for storing an optionally inserted set ofharmonic coefficients, a switch for connecting said generation means toutilize the harmonic coefficients from said storage means when saidswitch is in one position and for connecting sAid generation means toutilize a set of harmonic coefficients provided in the instrument whensaid switch is in another position, and an external data insertiondevice for entering said optional set of harmonic coefficients into saidstorage means.
 3. In a musical instrument of the type includinggeneration means for synthesizing a musical waveshape by computing inreal time the amplitudes at successive sample points of that waveshape,and a converter for converting said waveshape amplitudes to musicalsignals as the computations are carried out, said generation meansincluding first circuitry for individually calculating the constituentFourier components of that musical waveshape, and an accumulator forsumming these Fourier components to obtain each waveshape amplitude therelative amplitudes of said Fourier components with respect to eachother being established by a set of harmonic coefficients utilized bysaid first circuitry, each harmonic coefficient having the same order asthe corresponding Fourier component, the improvement for dynamicallymodifying the voice of the produced musical signals, comprising: storagemeans for storing voice modification data each associated with a Fouriercomponent of corresponding order, each such voice modification datadesignating the extent to which the relative amplitude of thecorresponding Fourier component should be altered, access control meansfor supplying each voice modification data from said storage means inunison with calculation of the Fourier component of corresponding order,and modification means for modifying the harmonic coefficient ofcorresponding order in accordance with said supplied voice modificationdata, the modified harmonic coefficients being utilized by saidgeneration means to establish the relative amplitude of thecorresponding Fourier component.
 4. A musical instrument according toclaim 3 wherein said voice modification comprises addition of atransient voice, and wherein; said storage means comprises a registercontaining a single transient voice related harmonic coefficient of aspecified order, wherein said access control means comprises acomparator for comparing the order of the Fourier component presentlybeing calculated with the order of said single transient voice relatedcoefficient, and gate means for supplying said transient voice relatedcoefficient from said register to said modification means when saidcomparator detects identity between the compared orders, and whereinsaid modification means comprises an adder for adding said transientvoice related coefficient to the harmonic coefficient of correspondingorder.
 5. A musical instrument according to claim 4 wherein saidtransient voice related coefficient consists of a binary word having asingle binary ''''1'''' bit, the position of said 1-bit in said wordestablishing the relative amplitude of the transient voice, furthercomprising: transient voice amplitude control means for altering theposition of said single 1-bit in said register to control the relativeamplitude of said transient voice.
 6. A musical instrument according toclaim 5 wherein said register comprisies a shift register, and whereinamplitude control means comprises; shift means for shifting the contentsof said register at controlled time intervals.
 7. A musical instrumentaccording to claim 3 wherein said voice modification comprises additionof a transient voice, wherein said storage means contains a set oftransient voice related harmonic coefficients of different order, andwherein said modification means comprises an adder for adding eachsupplied transient voice related coefficient to the harmonic coefficientof corresponding order.
 8. A musical instrument according to claim 7wherein said transient voice produces a chiff effect, and wherein theonly transient voice related harmonic coefficient of non-negligiblevalue in said set is tHat coefficient associated with the Fouriercomponent contributing a third or fifth harmonic to said musicalwaveshape.
 9. A musical instrument according to claim 7 together with;means for altering the values of the transient voice related harmoniccoefficients contained in said storage means at controlled timeintervals.
 10. A musical instrument according to claim 3 wherein saidvoice modification comprises modification of the harmonic content ofsaid musical signals, wherein: said storage means comprises a shiftregister storing a set of binary bits each associated with a particularFourier component order, the value of each bit designating whether ornot the correspondidng Fourier component is to be included in thewaveshape amplitude summation, and wherein said modification meanscomprises a gate for enabling the associated harmonic coefficient to beutilized by said generation means if the corresponding bit is of onebinary value, and for providing a zero-valued harmonic coefficient tosaid generation means if the corresponding bit is of the other binaryvalue.
 11. A musical instrument according to claim 10 furthercomprising; means for loading different sets of binary bits into saidshift register at controlled time intervals, so that during attack thevalue nmin is decreased progressively with time, where nmin is thelowest Fourier component order included in the waveshape amplitudesummation during attack, and so that during decay the value nmax isincreased progressively with time, where nmax is the highest Fouriercomponent order included in the summation during decay.
 12. A musicalinstrument according to claim 3 wherein said voice modificationcomprises modulation of the harmonic content of said musical signals,wherein said storage means comprises a plurality of memories eachcontaining a set of attack/decay amplitude scale factors associated witha respective Fourier component order, wherein said access control meansis time controlled to access different scale factors from said memoriesat different times during waveshape generation, and wherein saidmodification means comprises a scaler for multiplying each harmoniccoefficient by the scale factor currently accessed from the memory thatstores factors of corresponding order.
 13. A musical instrumentaccording to claim 3 together with an external data insertion deviceoperatively connected to said first circuitry for providing said set ofharmonic coefficients to said musical instrument, said provided harmoniccoefficients being utilized by said generation means to establish thetonal quality of the generated musical signals.
 14. In a musicalinstrument of the type having: first means for computing the Fouriercomponents of a periodic complex waveshape at successive sample points,said Fourier components being computed separately for each sample point,said computations occurring at a clock rate independent of the period ofsaid waveshape, the computed Fourier components having differentrespective orders n between a minimum order nmin and a maximum ordernmax, accumulator means for adding the component values calculated bysaid first means to obtain the waveshape amplitude at said each samplepoint, and means for providing musical notes from the waveshapeamplitudes obtained in said accumulator means, and wherein said firstmeans comprises: note selection means including keyboard switches forselecting a frequency number establishing the separation betweensuccessive sample points, said number thereby establishing the period ofthe resultant musical note, a note interval adder, operative during eachsuccessive amplitude computation, to add said selected number of the sumpreviously contained in said note interval adder, the resultant contentsof said note interval adder representing the sample point for which saidwaveshape amplitude Is computed, means for obtaining a trigonometricvalue, the argument of said trigonometric value being the product of thesaid sample point designated by the contents of said note interval addertimes the order of the Fourier component presently being calculated, aharmonic coefficient memory storing a set of harmonic coefficient valuesdesignating the relatiive amplitude of each constituent Fouriercomponent of a principal tone with respect to the amplitudes of theother constituent Fourier components of that tone, and a multiplier formultiplying each obtained trigonometric value by the modified harmoniccoefficient of order corresponding to that of the Fourier componentpresently being calculated the products of such multiplication being thecalculated Fourier component values which are added by said accumulatormeans to obtain the sample point amplitudes, the improvement formodifying the tonal quality of the provided musical notes duringportions of note production, comprising; attack and decay signal means,responsive to depression and release of any keyboard switch, forproviding respective start of attack and start of decay signals, andmodification means for modifying the harmonic coefficients accessed fromsaid harmonic coefficient memory as a function of time during the attackor decay periods initiated respectively by said start of attack andstart of decay signals, the resultant modified harmonic coefficientsbeing supplied to said multiplier.
 15. A musical instrument according toclaim 14 wherein said tonal quality is modified by the addition to saidprincipal tone of a transient voice, said modification means comprising:a storage device containing at least one transient-voice-relatedharmonic coefficient, and an adder for adding eachtransient-voice-related harmonic coefficient to theprincipal-tone-related harmonic coefficient of corresponding order toobtain a modified harmonic coefficient that is utilized by saidmultiplier during calculation of the Fourier component value ofcorresponding order.
 16. A musical instrument according to claim 15together with; a transient duration counter, responsive to the contentsof said note interval adder, for counting the number of fractionalcycles of the provided musical note that have been generated sinceoccurrence of said start of attack signal, and means for changing thevalues of the transient-voice-related harmonic coefficients in saidstorage device in response to the count of said transient durationcounter.
 17. A musical instrument according to claim 16 wherein saidstorage device is a register storing a single transient-voice-relatedharmonic coefficient that is added to the principal-voice-relatedharmonic coefficient of corresponding order for a period of timeestablished by said transient duration counter, resulting in theproduction of a transient voice of substantially sinusoidal waveshape.18. A musical instrument according to claim 17 wherein said singletransient-voice-related harmonic coefficient consists of a binary numberhaving a single binary 1 bit, together with clock means for shifting theposition of said single 1 bit in said number, and hence changing therelative amplitude of the transient voice, as a function of time.
 19. Amusical instrument according to claim 15 together with; an attack scalefactor memory containing a set of attack scale factors that establishthe amplitude envelope of the generated principal tone during attack,attack memory access control circuitry, initiated by said start ofattack signal and responsive to the number of cycles of the generatedtone, for accessing successive attack scale factors from said scalefactor memory, and a scaler for scaling the modified harmoniccoefficients by the scale factor value currently accessed by saidcontrol circuitry prior to utilization of said modified harmoniccoefficient by said multiplier.
 20. A musical insTrument according toclaim 19 wherein the summed transient-and principal-voice-relatedharmonic coefficients from said adder are scaled by said scaler, so thatthe combined principal tone and transient voice both have an envelopeestablished by said stored attack scale factors.
 21. A musicalinstrument according to claim 19 wherein only saidprincipal-voice-related harmonic coefficient is scaled by said scalerprior to addition to said transient-voice-related harmonic coefficientin said adder, so that only the principal tone but not the transientvoice has an envelope established by said stored attack scale factors.22. A musical instrument according to claim 14 wherein said tonalquality is modified by selectively, programmatically deleting certainFourier components from each waveshape amplitude computation duringattack and decay, and wherein said modification means comprises: astorage device containing a single binary word having one binary digitassociated with each Fourier component that can be included in eachwaveshape amplitude computation, a gate, operative as each harmoniccoefficient is accessed from said harmonic coefficient memory, forpermitting said accessed harmonic coefficient to be utilized by saidmultiplier if the associated binary digit is of one binary value and forproviding a zero-valued harmonic coefficient to said multiplier if theassociated binary digit is of the other binary value, and timecontrolled means, initiated by said start of attack or start of decaysignals, for selectively altering said single binary word at certaintime intervals during attack and/or decay.
 23. A musical instrumentaccording to claim 22 wherein: said storage device comprises a shiftregister that is shifted in unison with the accessing of said harmoniccoefficient memory, the contents of one position of said shift registerbeing used to control the enabling of said gate, and wherein said timecontrolled means comprises a counter, reset by said start of attack andstart of decay signals and responsive to the contents of said noteinterval adder, that counts the number of cycles of fractional cycles ofthe principal tone that have been generated since the start of attack ordecay, and load circuitry for entering different binary words into saidshift register when the counter reaches certain preset count values. 24.A musical instrument according to claim 23 wherein said load circuitryenters data into said shift register that cause the value of the minimumorder nmin to be decreased progressively during attack, and that causethe value of the maximum order nmax to be decreased progressively duringdecay.
 25. A musical instrument according to claim 24 further comprisingcircuitry for preventing such alteration of constituent Fouriercomponent minimum and maximum order when a principal tone having asubstantially sinusoidal waveshape is being generated.
 26. A musicalinstrument according to claim 14 wherein said modification meanscomprises; separate attack/decay scale factor memories each containing aset of attack/decay amplitude scale factors associated with a respectiveFourier component order, time dependent access control means, initiatedby said start of attack and start of decay signals, for accessingdifferent scale factors from each attack/decay scale factor memory atdifferent times during attack and decay, and a harmonic coefficientscaler for multiplying each harmonic coefficient accessed from saidharmonic coefficient memory by the currently accessed attack/decay scalefactor of corresponding order.